Mixed-mode Integration for Real-time Simulation

The new possibilities of multi-domain hierarchical modelling often lead to models with both fast and slow parts. In this paper a new approach to simulate such systems is discussed that is especially useful in real-time applications. Mixed-mode integration represents a middle course between implicit and explicit integration. The main idea is to split up the system into a fast and a slow part and to apply implicit discretization only to the fast part. The partitioning of the system can be performed offline using a newly developed automatic selection routine, before real-time simulation starts. Mixed-mode integration was applied to several Modelica models from different fields, e.g. models of a diesel engine and an industrial robot and tested using Dymola. Speedup factors from about 4-16 were recorded. In this paper, mixed-mode integration is introduced, the selection routine is described and numerical results are presented